Apparatus and method for multiple primary bridge resonant converters

1. A converter comprising:

an input stage coupled to a power source, wherein the input stage comprises a plurality of power switches;

a first resonant tank coupled to the plurality of power switches, wherein the first resonant tank is of a first Q value;

a second resonant tank coupled to the plurality of power switches, wherein the second resonant tank is of a second Q value, and wherein the first Q value is greater than the second Q value, and wherein the first resonant tank is configured to be enabled and the second resonant tank is configured to be disabled during a startup process;

a transformer coupled to the input stage; and

an output stage coupled to the transformer.

2. The converter of claim 1 , wherein:

the input stage comprises a first full bridge switching network and a second full bridge switching network, and wherein:

the first full bridge switching network and the second full bridge switching network are connected in parallel and coupled between the power source and the transformer; and

the first full bridge switching network is coupled to a first primary side winding of the transformer and the second full bridge switching network is coupled to a second primary side winding of the transformer.

3. The converter of claim 2 , wherein:

the first resonant tank comprises a first inductor and a first capacitor, and wherein the first inductor and the first capacitor are connected in series and coupled between the first full bridge switching network and the first primary side winding of the transformer; and

the second resonant tank comprises a second inductor and a second capacitor, and wherein the second inductor and the second capacitor are connected in series and coupled between the second full bridge switching network and the second primary side winding of the transformer.

4. The converter of claim 1 , wherein the input stage comprises:

a first switch and a second switch connected in series and coupled between two terminals of the power source;

a third switch and a fourth switch connected in series and coupled between the two terminals of the power source; and

a fifth switch and a sixth switch connected in series and coupled between the two terminals of the power source.

5. The converter of claim 4 , wherein:

the first resonant tank comprises a first inductor and a first capacitor, and wherein the first inductor and the first capacitor are connected in series and coupled between a first terminal of a primary side winding of the transformer and a common node of the first switch and the second switch;

the second resonant tank comprises a second inductor and a second capacitor, and wherein the second inductor and the second capacitor are connected in series and coupled between the first terminal of the primary side winding of the transformer and a common node of the fifth switch and the sixth switch; and

a second terminal of the primary side winding of the transformer is coupled to a common node of the third switch and the fourth switch.

6. The converter of claim 4 , wherein:

the first resonant tank comprises a first inductor and a first capacitor; and

the second resonant tank comprises a second inductor and the first capacitor, and wherein:

the first inductor has a first terminal coupled to a common node of the first switch and the second switch;

the second inductor has a first terminal coupled to a common node of the fifth switch and the sixth switch and a second terminal coupled to a second terminal of the first inductor; and

a primary side winding of the transformer and the first capacitor are connected in series and coupled between a common node of the first inductor and the second inductor, and a common node of the third switch and the fourth switch.

7. The converter of claim 4 , wherein:

the first resonant tank comprises a first inductor and a first capacitor; and

the second resonant tank comprises the first inductor and a second capacitor, and wherein:

the first capacitor has a first terminal coupled to a common node of the first switch and the second switch;

the second capacitor has a first terminal coupled to a common node of the fifth switch and the sixth switch, and a second terminal coupled to a second terminal of the first capacitor; and

a primary side winding of the transformer and the first inductor are connected in series and coupled between a common node of the first capacitor and the second capacitor, and a common node of the third switch and the fourth switch.

8. The converter of claim 1 , wherein:

the first Q value is in a range from about 0.2 to about 5; and

the second Q value is in a range from about 0.2 to about 5.

9. A method comprising:

providing a resonant converter, wherein the resonant converter comprises:

an input stage coupled to a power source, wherein the input stage comprises a plurality of power switches;

a first resonant tank coupled to a first portion of the plurality of power switches, wherein the first resonant tank is of a first Q value;

a second resonant tank coupled to a second portion of the plurality of power switches, wherein the second resonant tank is of a second Q value;

a transformer coupled to the first resonant tank and the second resonant tank; and

an output stage coupled to the transformer;

enabling the first portion of the plurality of power switches and disabling the second portion of the plurality of power switches during a startup process of the resonant converter; and

enabling the second portion of the plurality of power switches after an output voltage of the resonant converter is greater than a first predetermined threshold and a load current of the resonant converter is greater than a second predetermined threshold.

10. The method of claim 9 , wherein:

the first portion of the plurality of power switches and the first resonant tank form a first resonant converter having the first Q value; and

the second portion of the plurality of power switches and the second resonant tank form a second resonant converter having the second Q value, and wherein the first Q value is greater than the second Q value.

11. The method of claim 9 , further comprising:

detecting the load current of the resonant converter; and

disabling the second portion of the plurality of power switches when load current is less than the second predetermined threshold.

12. The method of claim 9 , further comprising:

in response to a load increase, enabling the second portion of the plurality of power switches; and

in response to a load drop, disabling the second portion of the plurality of power switches.

13. The method of claim 9 , wherein:

the first portion of the plurality of power switches is a first full bridge switching network; and

the second portion of the plurality of power switches is a second full bridge switching network, and wherein:

the first full bridge switching network and the second full bridge switching network are connected in parallel and coupled between the power source and the transformer.

14. The method of claim 9 , wherein:

the first predetermined threshold is about 90% of a steady-state output voltage of the resonant converter; and

the second predetermined threshold is about 10% of a full load current of the resonant converter.

15. A method comprising:

providing a dual primary bridge resonant converter, wherein the dual primary bridge resonant converter comprises:

a first full bridge switching network; and

a first resonant tank coupled to the first full bridge switching network, wherein the first resonant tank is of a first Q value;

a second full bridge switching network, wherein the second full bridge switching network and the first full bridge switching network are connected in parallel; and

a second resonant tank coupled to the second full bridge switching network, wherein the second resonant tank is of a second Q value;

a transformer coupled to the first resonant tank and the second resonant tank; and

an output stage coupled to the transformer; and

enabling the first full bridge switching network and disabling the second full bridge switching network during a startup process of the dual primary bridge resonant converter.

16. The method of claim 15 , further comprising:

enabling the second full bridge switching network after an output voltage of the dual primary bridge resonant converter is greater than a first predetermined threshold.

17. The method of claim 15 , further comprising:

enabling the second full bridge switching network when a load current of the dual primary bridge resonant converter is greater than a second predetermined threshold.

18. The method of claim 15 , further comprising:

in response to a load increase, enabling the second full bridge switching network; and

in response to a load drop, disabling the second full bridge switching network.

19. The method of claim 15 , wherein:

the first Q value is greater than the second Q value.

20. The method of claim 15 , wherein:

the first full bridge switching network and the first resonant tank form a first LLC resonant converter; and

the second full bridge switching network and the second resonant tank form a second LLC resonant converter, wherein the first LLC resonant converter and the second LLC resonant converter are connected in parallel.